This research project essentially involves an analysis of B lymphocyte and macrophage differentiation through a study of a series of murine tumor cell lines, which show various degrees of maturation arrest. Analysis of immunoglobulin synthesis, membrane expression, and secretion, provides definitive characterization of various differentiation stages. Further resolution of murine immunoglobulin allotypes will provide valuable reagents for analysis of Ig expression. Many alloantigens and hybridoma defined cell surface components are becoming available for further definition of subpopulations of cells in both B cell and macrophage lineages, and these components will be used in a general study of differentiation arrest, intratumor heterogeneity, and potential for further induction of differentiation in these cell lines. Particular emphasis is being placed on functional properties of these cell lines and their value as models for better isolating and characterizing gene products that are expressed at specific differentiation stages. Precise analysis of the differentiation state of these tumors will in turn render them as invaluable models for analysis of genetic recombination in B cell differentiation.